**Acknowledgements**

The part of theoretical study and computer simulation of the present work was conducted in Research Hub for Advanced Nano Characterization, The University of Tokyo, supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

HITACHI SR-11000 and SGI Altix ICE 8400EX super computer systems of the Institute for Solid State Physics of The University of Tokyo were used for the computer simulations.

The preliminary experiments were performed at AR-BL3A of the Photon Factory AR under the approval of the Photon Factory Program Advisory Committee (Proposals No. 2003G202 and No. 2003G203). The main experiments were performed at BL09XU of SPring-8 under the approval of Japan Synchrotron Radiation Research Institute (JASRI) (Proposals No. 2005B0714 and No. 2009B1384).

The present work is one of the activities of Active Nano-Characterization and Technology Project financially supported by Special Coordination Fund of the Ministry of Education, Culture, Sports, Science and Technology of the Japan Government.

The authors are indebted to Dr. Y. Ueji Dr. X.-W. Zhang and Dr. G. Ishiwata for their technical support in the present experiments and also to Professor Emeritus S. Kikuta for his encouragements and fruitful discussions for the present work.

### **Author details**

#### Kouhei Okitsu

*Nano-Engineering Research Center, Institute of Engineering Innovation, Graduate School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan*

#### Yasuhiko Imai and Yoshitaka Yoda

*Japan Synchrotron Radiation Research Institute, SPring-8, 1-1-1 Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan*

#### **7. References**

